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Exp. 381 Sampling and Measurement Plan

 
 

Offshore sampling and measurements plan

Owing to the nature of MSP expeditions, there is commonly limited laboratory space offshore, and as such there is no splitting of the cores at sea. The scientific analyses undertaken onboard are consequently limited to a subset of the expedition dataset. Offshore scientific activities include those essential for core curation, securing head space sediment samples and samples for pore-water chemistry, sampling for shipboard biostratigraphy, measurement of ephemeral properties including physical properties, and downhole logging.

This sampling and meas­ure­ments plan is sub­ject to amend­ment ac­cord­ing to the sci­entific needs/​in­terests of the Sci­ence Party and/​or op­er­a­tional con­straints. Routine meas­ure­ments and core flow will be un­der­taken in line with the IODP-Mission Specific Platform (MSP) standard measurements pro­ced­ures.

The following measurements will be carried out offshore:

Curation
mobile core curation laboratory container will be on board the drilling plat­form. Cur­a­torial representatives will have del­eg­ated re­spons­ib­il­ity in the ab­sence of the ESO Cur­a­tion and Laboratory Man­ager and IODP Cur­ator for the Bre­men Core Re­pos­it­ory (BCR) and MSPs, Dr. Ur­sula Röhl. The cores will be curated and labelled, and stored in a temperature-controlled reefer (~4°C). There will be no split­ting of the cores at sea with the ma­jor­ity of sci­entific ana­lyses being conducted dur­ing the Onshore Science Party (OSP) in Bremen (sched­uled to start 31st January 2018).

Core description
Prior to being stored in the temperature-controlled reefer, the cores will be described (through the liner) by members of the Science Party, and data will be recorded in the offshore Drilling Information System (ExpeditionDIS) database.

Core catcher (CC) samples will be col­lec­ted on board at in­ter­vals dic­tated by the length of the core bar­rels used (1.5 m or 3 m). The core catcher will be described and sampled for ini­tial sed­i­mento­lo­gical and micropaleontological analysis, and images of the CC will be taken.

If no core catcher sample is re­covered, a sample from the lower end of each core will be taken for ship­board ana­lysis. Thin sec­tion bil­lets may be taken in rep­res­ent­at­ive sec­tions for pre­par­a­tion in ad­vance of the OSP, as advised by the offshore sedimentologists.

Geochemistry
Headspace sediment samples will be taken from the fresh cut end of a core section on a routine basis (in suit­able li­tho­lo­gies and dependent on core recovery) and stored in the reefer container for onshore analysis.

In suit­able li­tho­lo­gies, pore-water samples (e.g. squeez­ers and/​or rhizone mois­ture samplers) will be taken on a routine basis. Pore-wa­ter will be ex­trac­ted im­me­di­ately from cores and ephemeral properties (e.g. sa­lin­ity, pH, al­ka­lin­ity and am­mo­nia) will be ana­lyzed. Sample splits for on­shore ana­lysis (e.g. cations, sulf­ide, 13C) will be pre­pared and pre­served whilst off­shore and stored in the reefer container.

It will be possible to take reference samples of the drill mud and the pump water if requested.
 
Core physical properties
Tem­per­at­ure-equi­lib­rated cores will be meas­ured on the drilling plat­form in a con­tain­er­ized labor­at­ory util­iz­ing a multi-sensor core logger (MSCL). The MSCL will col­lect gamma dens­ity, P-wave ve­lo­city (where acous­tic coup­ling is pos­sible), non-con­tact elec­trical res­istiv­ity, mag­netic sus­cept­ib­il­ity and natural gamma radiation data. QA/​QC checks will be car­ried out off­shore, in­clud­ing regular measurement of cal­ib­ra­tion stand­ards to mon­itor sensor pre­ci­sion and ac­cur­acy.

Small penetrometer devices will also be available offshore for acquisition of penetration resistance data: if appropriate and as requested.

Downhole logging
Su­per-slim­line log­ging tools will be de­ployed to col­lect down­hole log­ging data. In addition, downhole measurements of the in situ formation temperature will be acquired during coring operations for each hole.

The tool suite available for Expedition 381 includes spectral and total gamma ray, P-wave sonic velocity, S-wave sonic velocity, acoustic and optical borehole imaging, electrical resistivity, magnetic susceptibility, hydrogeological measurements (fluid conductivity, pH, eH, temperature, and dissolved oxygen), caliper and flow meter. 

Spectral gamma ray, P-wave sonic, magnetic susceptibility and caliper have been identified as the priority measurements for this project.

The proposed downhole logging program consists of the fol­low­ing meas­ure­ments:
• Through-pipe: spec­tral gamma ray (standalone). 
• Open hole: dual laterolog (standalone); gamma ray + sonic + acoustic televiewer (stacked); gamma ray + caliper + magnetic susceptibility (stacked); spectral gamma ray; and/or conductivity + magnetic susceptibility depending on time and data quality from previous runs.

Other down­hole log­ging meas­ure­ments (to be ac­quired in open hole) will be in­cluded in the log­ging pro­gram de­pend­ing on hole con­di­tions, op­er­a­tional pro­gress and pre­lim­in­ary sci­entific res­ults.

Onshore sampling and measurements plan

The OSP will be un­der­taken at the IODP Bre­men Core Re­pos­it­ory (BCR) and labor­at­ories at MARUM - Center for Marine Environmental Sciences, University of Bremen, and the De­part­ment of Geosciences, Uni­versity of Bre­men.
The fol­low­ing fa­cil­it­ies will be avail­able to the Science Party members during the OSP:

  • Core splitting: the cores will be split into a working and an archive half in line with IODP procedures.
  • Core description: ESO will provide IODP standard facilities for core description, including access to a CoreWall visualisation system. Core description will be undertaken on the archive half of the cores. For data entry, ESO will employ a version of the offshore Drilling Information System (DIS), called “ExpeditionDIS”, which is comparable with others being used in IODP.
  • Digital line-scan imaging: high resolution images of the archive half of the cores will be acquired utilising an XRF-core scanner mounted with a line-scan camera.
  • Thin section and smear slide preparation: as requested.
  • Inorganic geochemistry: whole-rock and pore fluid chemistry; inductively coupled plasma–optical emission spectrometry (ICP-OES); ion chromatography (IC); energy dispersive X-ray fluorescence (ED XRF); and total carbon (TC) / total organic carbon (TOC) content (LECO CS analyzer) / carbonate content.
  • Biostratigraphy: facilities to wash and sieve samples including controlled access to the HF lab at MARUM for palynology sample processing, microscopes including options for image capture.
  • X-ray diffraction analysis (XRD): bulk mineralogy.
  • Paleomagnetic measurements: natural remnant magnetism (NRM) with stepwise demagnetization (2G longcore cryogen magnetometer) or samples (robot system which feeds up to 100 adapted sample cubes).
  • Physical properties measurements:
    • Thermal conductivity on whole cores will be acquired by ESO staff prior to the OSP at MARUM utilising a needle probe system.  Additional standard IODP physical properties measurements may be undertaken on whole cores at this time in the event offshore datasets are incomplete. This may be owing to time (natural gamma radiation) or permitting issues (gamma density). 
    • Physical properties of discrete samples: P-wave velocity and moisture and density properties (MAD) including: wet bulk density; grain density; porosity; and void ratio. For MAD measurements, core samples will be oven-dried (60° ± 5°C), the dried sample volume will then be quantified using a Quantachrome penta-pycnometer with sample masses being measured using a high-precision balance.
    • Undrained shear strength (Su): measurements utilizing a torvane, pocket penetrometer, and/or fall cone (on request) can be undertaken on the working half of the core.
    • Color reflectance: measurements acquired using a MSCL mounted with a Minolta spectrophotometer.
  • Core sampling: A detailed sampling plan will be devised following review of all revised sample requests by the Sample Allocation Committee (SAC), prior to the start of the OSP and after the scientists have submitted their revised sample requests.